The RFCC process is a process for producing LPG, gasoline, diesel, naphtha and the like by further conducting a catalytic cracking reaction on a heavy residual oil that remains after the fractionation of a crude oil. According to the RFCC process, LPG, gasoline, diesel and the like are repoduceed by re-cracking the heavy residual oil which itself does not contain fuel. Thus, these are referred to as a ground oilfield and applied to an important advanced equipment of refinery companies.
Products which can be obtained through the RFCC process, include various substances based on the boiling point, such as LPG, gasoline and diesel, but the main target product to date is gasoline. In the current RFCC process, the yield of gasoline is approximately 50% by weight. Further, considering the MTBE and alkylate resulting from the C4 product obtained in the RFCC process, the yield of gasoline is in realty more than 60% by weight.
However, as the demand for gasoline is decreasing and shale-gas based gasoline alternative energy sources are developed, gasoline prices are falling continuously, and this trend is expected to be more extreme in the future.
In this regard, there is a need to change the target product of the RFCC process to substances other than gasoline. The substance which can be the most practical alternative can be seen as diesel.
On the other hand, the catalyst for conventional RFCC processes has been classified as a zeolite and a matrix, and the matrix was composed mainnly of kaolin clay. The zeolite and matrix have functions different from each other in the catalyst. If a petroleum feedstock containing a heavy residual oil is used, the cracking reaction occurs primarily a matrix having mesopores or macropores. Thus, through the primary cracking reaction, the petroleum feedstock, which has become small enough to enter the micropores of the zeolite, enters the zeolite micropores, the cracking reaction proceeds and the heavy residual oil is converted to LPG, gasoline and the like.
In other words, in the matrix, diesel (LCO, HCN) and heavy gasoline (HCN) are selectively produced through the pre-cracking of the heavy residual oil. In the zeolite, some LPG, light gasoline (LLCN, LCN) are selectively produced.
Depending on the components of the catalyst, the cracking functions of the catalysts are different from each other and so the components of the catalyst can be properly selected, thus controling the cracking performance. In other words, in order to obtain diesel, for which demand is recently increasing, the diesel yield can be maximized by not introducing zeolite into the catalytic cracking catalyst.
However, the catalytic cracking catalyst composed of only the matrix without introducing zeolite has two problems as follows:
First, the coke yield is lowered. Zeolite produces a catalytic coke while producing gasoline, LPG and the like in the RFCC process. Accordingly, if zeolite is not present in the catalyst, the generation of catalytic coke is reduced and the overall coke yield is lowered. The RFCC process maintains the heat balance through the coke. Therefore, if the coke yield is lowered, it may lead to a problem that the operation cannot be substantially performed.
Second, the cracking function is decreased due to external acid sites in zeolite. Since zeolites are materials having micropores, gasoline, LPG and the like can be selectively produced, but in addition there exists a pre-cracking function due to the external acid sites in zeolite. Accordingly, if zeolite is not present in the catalyst, the cracking function due to the external acid sites cannot be expected. There is a problem that the cracking performance generally falls.